The disclosure of Japanese Patent Application No. 2000-065449 filed on Mar. 9, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to methods and a valve characteristic control apparatus of an internal combustion engine for variably controlling the valve characteristic of an engine valve in accordance with the operation state of the engine.
2. Description of the Related Art
As a valve characteristic control apparatus, an apparatus described in Japanese Patent Application Laid-Open No. 8-177434, as for example, is known. This apparatus includes a valve lift-varying mechanism that allows variation of the amount of valve lift of an engine valve, and a valve timing-varying mechanism that allows variation of the valve timing. If either one of the varying mechanisms has a fault, the following control is performed. That is, with regard to the valve lift-varying mechanism, the mechanism is switched to a low speed type cam. With regard to the valve timing-varying mechanism, a control is performed such that the relative rotation phase of a camshaft is shifted to retarded side. For this control, the presence or absence of a fault of the valve lift-varying mechanism is diagnosed by detecting the hydraulic pressure of hydraulic oil needed for the switching of a cam (low speed type cam, and a high speed type cam) of the mechanism. The presence or absence of a fault of the valve timing-varying mechanism is diagnosed by detecting the rotation phase of a cam (camshaft).
However, as a valve lift-varying mechanism as described above, a mechanism has recently been proposed in which the camshaft is displaceable in the directions of an axis of the camshaft, and in which the camshaft is provided with a generally termed three-dimensional cam, that is, a cam whose cam lobe is continuously varied from one end to the other end thereof in the directions of the axis. According to such a three-dimensional cam type valve lift-varying mechanism, it becomes possible to continuously change the amount of lift of the valve in accordance with the operation state of the engine.
However, in such a three-dimensional cam type valve lift-varying mechanism, the variable control itself is not binary, and is performed with continuous values. Therefore, for the diagnosis regarding the presence/absence of a failure of the mechanism, the diagnostic technique employed by the aforementioned apparatus cannot be simply applied.
Furthermore, technologies have recently been proposed which more suitably maintain the engine characteristic of the internal combustion engine by constructing a valve characteristic control apparatus through a combination of three-dimensional cam type valve lift-varying mechanism and a valve timing-varying mechanism as described above. In the valve characteristic control apparatuses constructed by combining a valve lift-varying mechanism and a valve timing-varying mechanism, the following problems are unignorable with regard to the fault diagnosis.
That is, for example, in a valve characteristic control apparatus employing a cam angle sensor, the fault diagnosis regarding the valve timing-varying mechanism becomes difficult in a relatively early period as the camshaft is displaced by the valve lift-varying mechanism. Furthermore, since both mechanisms use continuous values for their respective variable controls, it is not easy to identify which one of the mechanisms has an abnormality if any abnormality occurs.
Accordingly, it is an object of the invention to provide methods and a valve characteristic control apparatus of an internal combustion engine that are capable of precisely diagnosing whether there is an abnormality even with regard to a three-dimensional cam type valve lift-varying mechanism.
In accordance with a first aspect of the invention, a valve characteristic control apparatus of an internal combustion engine includes a camshaft provided with a three-dimensional cam having a cam profile that continuously changes in a direction of an axis of the cam, a valve lift-varying mechanism that allows an amount of valve lift of an engine valve to be varied in accordance with a displaced position of the camshaft in the direction of the axis of the cam, a sensor for detecting valve lift and a controller that receives a signal from the sensor and diagnoses that there is an abnormality of the valve lift-varying mechanism, provided that a deviation between an actually detected amount of valve lift and a target amount of valve lift of the engine valve is greater than a predetermined value and that an amount of change in the actually detected amount of valve lift is less than a predetermined value.
According to the above-described valve lift-varying mechanism, the valve characteristic of the engine valve can be suitably variably controlled by continuously displacing the camshaft provided with the three-dimensional cam in the direction of the axis thereof. However, with regard to the continuous displacement control of the camshaft in the direction of the axis, the target amount of valve lift and the actually detected amount of valve lift are not always equal, due to a response delay in the control.
In this respect, according to the above-described construction, it becomes possible to precisely diagnose that there is an abnormality, that is, an operation abnormality of the valve lift-varying mechanism, based on a determination that the amount of change in the actually detected amount of valve lift is less than the predetermined value even though there is a great deviation between the target amount of valve lift and the actually detected amount of valve lift. In other words, the abnormality is based on a determination that the valve lift characteristic is not in the course of changing.
In accordance with a second aspect of the invention, a valve characteristic control apparatus of an internal combustion engine includes a camshaft provided with a three-dimensional cam having a cam profile that continuously changes in a direction of an axis of the cam, a valve lift-varying mechanism that allows an amount of valve lift of an engine valve to be varied in accordance with a displaced position of the camshaft in the direction of the axis of the cam, at least one sensor that detects actual valve lift and a controller that receives a signal from the at least one sensor and diagnoses that there is an abnormality of the valve lift-varying mechanism, provided that an amount of change in actually detected amount of valve lift of the engine valve is greater than a predetermined value although a state where an instruction to retain the amount of valve lift is outputted has continued for a predetermined duration.
During the state where the instruction is outputted to retain the valve characteristic for a predetermined duration, the amount of change in the actually detected amount of valve lift is considered to become xe2x80x9c0xe2x80x9d if the valve lift-varying mechanism is normally operating. In this respect, according to the above-described construction, it becomes possible to precisely determine that there is an abnormality, that is, a retainment control abnormality, provided that the amount of change in the amount of valve lift actually detected during that state is greater than the predetermined value.
In accordance with a third aspect of the invention, a valve characteristic control apparatus of an internal combustion engine includes a camshaft provided with a three-dimensional cam having a cam profile that continuously changes in a direction of an axis of the cam, a valve lift-varying mechanism that allows an amount of valve lift of an engine valve to be varied in accordance with a displaced position of the camshaft in the direction of the axis of the cam, a sensor that detects an actual amount of valve lift and a controller that receives a signal from the sensor and diagnoses that there is an abnormality of the valve lift-varying mechanism, provided that a deviation between an actually detected amount of valve lift and a target amount of valve lift of the engine valve is greater than a predetermined value and that there is no abnormality in a retainment control system while in a state where an instruction to retain the amount of valve lift is outputted is present.
When the retainment instruction has been outputted and the retainment control system has no abnormality, the actually detected amount of valve is considered to have converged to the target amount of valve lift. In this respect, it is possible to precisely determine that there is an abnormality, that is, an operation abnormality of the valve lift-varying mechanism, provided that the deviation between the target amount of valve lift and the actually detected amount of valve lift is greater than the predetermined value although the retainment instruction has been outputted and the retainment control system has no abnormality.
In accordance with a fourth aspect of the invention a valve characteristic control apparatus of an internal combustion engine includes a camshaft provided with a three-dimensional cam having a cam profile that continuously changes in a direction of an axis of the cam, a valve lift-varying mechanism that allows an amount of valve lift of an engine valve to be varied in accordance with a displaced position of the camshaft in the direction of the axis of the cam, a sensor that detects actual valve lift and a controller that receives a signal from the sensor and diagnoses that there is an abnormality of the lift-varying mechanism, provided that a deviation between an actually detected amount of valve lift and a target amount of valve lift of the engine valve is greater than a predetermined value and that any one of conditions listed below is met: (a) an amount of change in the actually detected amount of valve lift is less than a predetermined value; (b) a state where an instruction to maintain the amount of valve lift is outputted continues for a predetermined duration; and (c) there is no abnormality in a retainment control system while the state here an instruction to maintain the amount of valve lift is outputted is present.
In this construction, it is possible to precisely diagnose whether the valve lift-varying mechanism has any one of various abnormalities, similarly to the diagnostic means in the first to third aspects. Furthermore, this construction greatly reduces the possibility of a failure in diagnosis regarding the various abnormalities.
In accordance with a fifth aspect of the invention, valve characteristic control apparatus of an internal combustion engine includes a camshaft provided with a three-dimensional cam having a cam profile that continuously changes in a direction of an axis of the cam, a valve lift-varying mechanism that allows an amount of valve lift of an engine valve to be varied in accordance with a displaced position of the camshaft in the direction of the axis of the cam, a valve timing-varying mechanism that allow a valve timing of the engine valve to be varied based on a change in a relative rotation phase between the camshaft and an engine output shaft, a first sensor that detects an actual amount of valve lift, a set of rotation sensors that detect an actual relative rotation phase between the camshaft and the engine output shaft, a controller that receives signals from the first sensor and the set of rotation sensors and diagnoses whether there is an abnormality based on an actually detected amount of valve lift and a target amount of valve lift of the engine valve, and an actually detected relative rotation phase and a target relative rotation phase between the camshaft and the engine output shaft, and the controller forces one of the valve lift-varying mechanism to a minimum engine valve lift side and the valve timing-varying mechanism to a most retarded valve timing side, if the controller determines that there is an abnormality and wherein after the controller forces one of the valve lift-varying mechanism and the valve timing-varying mechanism the controller diagnoses whether the abnormality still exists and if so, the controller distinguishes which one of the valve lift-varying mechanism and the valve timing-varying mechanism has the abnormality.
According to the above-described construction, even if the valve characteristic control apparatus is formed by a combination of the valve lift-varying mechanism and the valve timing-varying mechanism, that is, even if it is difficult to identify which one of the two mechanisms has a valve characteristic abnormality, the valve characteristic control apparatus is able to precisely identify which one of the valve lift-varying mechanism and the valve timing-varying mechanism has an abnormality in the valve characteristic in accordance with the content of the abnormality determined after one of the two mechanisms is forcibly driven in the above-described manner.
In the first to fifth aspects, the valve characteristic control apparatus may further include a controller that performs a foreign object removing process with respect to the valve lift-varying mechanism, if it is determined that the valve lift-varying mechanism has an abnormality.
One of the abnormalities related to the valve lift-varying mechanism is an operation failure caused by a metal chip or the like trapped in the mechanism, for example, in a hydraulic oil supply system, that is, a drive system. When such an abnormality occurs, the metal chip or the like can often be automatically removed by forcibly driving the mechanism.
In this respect, according to the above-described construction, after it is diagnosed that there is an abnormality, the recovery of the valve lift-varying mechanism to a normal state can be attempted by forcibly driving the mechanism.
Furthermore, in the aforementioned aspects, the controller may cause the execution of a fail-safe operation if the mechanism diagnosed as having an abnormality by the controller is the valve lift-varying mechanism. Furthermore, the fail-safe operation is at least one of increasing a fuel supplied to the engine, prohibiting a learning regarding an idle revolution speed control, prohibiting a learning regarding an air-fuel ratio feedback control, expanding a fuel-cut operation region, and upwardly shifting a fuel-cut return revolution speed.
In the above-described constructions, by performing the fail-safe operation after the it controller diagnoses that the valve lift-varying mechanism has an abnormality, a safety-mode operation of the engine can be realized.
It is also an object of this invention to provide methods of diagnosing abnormalities of a valve lift-varying mechanism.
It is also an object of this invention to provide methods of diagnosing a valve retainment control abnormality of a valve lift-varying mechanism.
It is also an object of this invention to provide methods of diagnosing whether an abnormality exists in a valve lift-varying mechanism and a valve timing-varying mechanism.